Yeah, that's not really a tab that switches like you can switch between like Drillers and Outposts. Funding is just a column.

You can see that, since you have 20 Npt more than your opponent and ally, there's a grey box for them under the funding column. (If the Npt difference is smaller than 20, you won't be able to fund them.)

Just tap that box and a popup will show, asking you for confirmation to start funding.